From before the auxiliary piston

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The

Bull Cornish engine is also still not infrequently seen in use. The Cornish engine of Great Britain averages a duty of about 45,000,000 pounds raised one foot high per 100 pounds of coal. More than double this economy has sometimes been attained.

[Illustration: FIG. 102.--Steam-Pump.]

A vastly simpler form of pumping-engine without fly-wheel is the now common "direct-acting steam-pump." This engine is generally made use of in feeding steam-boilers, as a forcing and fire pump, and wherever the amount of water to be moved is not large, and where the pressure is comparatively great. The steam-cylinder, _A R_, and feed-pump, _B Q_ (Fig. 102), are in line, and the two pistons have usually one rod, _D_, in common. The two cylinders are connected by a strong frame, _N_, and two standards fitted with lugs carry the whole, and serve as a means of bolting the pump to the floor or to its foundation.

The method of working the steam-valve of the modern steam-pump is ingenious and peculiar. As shown, the pistons are moving toward the left; when they reach the end of their stroke, the face of the piston strikes a pin or other contrivance, and thus moves a small auxiliary valve, _I_, which opens a port, _E_, and causes steam to be admitted behind a piston, or permits steam to be exhausted, as in the figure, from before the auxiliary piston, _F_, and the pressure within the main steam-chest

then forces that piston over, moving the main steam-valve, _G_, to which it is attached, admitting steam to the left-hand side of the main piston, and exhausting on the right-hand side, _A_. Thus the motion of the engine operates its own valves in such a manner that it is never liable to stop working at the end of the stroke, notwithstanding the absence of the crank and fly-wheel, or of independent mechanism, like the cataract of the Cornish engine. There is a very considerable variety of pumps of this class, all differing in detail, but all presenting the distinguishing feature of auxiliary valve and piston, and a connection by which it and the main engine each works the valve of the other combination.

In some cases these pumps are made of considerable size, and are applied to the elevation of water in situations to which the Cornish engine was formerly considered exclusively applicable. The accompanying figure illustrates such a pumping-engine, as built for supplying cities with water. This is a "compound" direct-acting pumping-engine. The cylinders, _A B_, are placed in line, working one pump, _F_, and operating their own air-pumps, _D D_, by a bell-crank lever, _L H_, connected to the pump-buckets by links, _I K_. Steam exhausted from the small cylinder, _A_, is further expanded in the large cylinder, _B_, and thence goes to the condenser, _C_. The valves, _N M_, are moved by the valve-gear, _L_, which is actuated by the piston-rod of a similar pair of cylinders placed by the side of the first. These valves are balanced, and the balance-plates, _R Q_, are suspended from the rods, _O P_, which allow them to move with the valves. By connecting the valves of each engine with the piston-rod of the other, it is seen that the two engines must work alternately, the one making a stroke while the other is still, and then itself stopping a moment while the latter makes its stroke.

Water enters the pump through the induction-pipe, _E_, passes into the pump-barrel through the valves, _V V_, and issues through the eduction-valves, _T T_, and goes on to the "mains" by the pipe, _G_, above which is seen an air-chamber, which assists to preserve a uniform pressure on that side the pump. This engine works very smoothly and quietly, is cheap and durable, and has done excellent duty.